Electrical insulating liquid (such as for example mineral oil) is commonly used in equipment that serves in the generating, transmitting, and distributing of electrical power. Such equipment generally includes transformers (sometimes called oil-immersed transformers), tap-changers and circuit breakers. In such equipment, the liquid acts as both heat dissipation and electrical insulating medium. When a fault occurs in such electrical equipment, fault gases may evolve in the insulating liquid.
The gases that are typically associated with specific fault types in such equipment are Hydrogen (H2), Carbon Dioxide (CO2), Carbon Monoxide (CO), Ethane (C2H6), Methane (CH4), Ethylene (C2H4) and Acetylene (C2H2). Analysis of one or more of such fault gases may be used to provide a diagnosis of the health of electrical equipment.
In this regard, various practical Dissolved Gas Analysis (DGA) applications have been previously suggested for detecting such fault gases in equipment that serves in the generating, transmitting and distributing of electrical power.
For example, U.S. Pat. No. 6,391,096 to Waters describes an apparatus for performing dissolved gas analysis on electrical insulating oil which makes use of a gas chromatograph to analyze the fault gases. The apparatus includes a tubular membrane extractor column for extracting the fault gases from the oil, where the column includes a plurality of composite hollow fiber tubes coated with a thin layer of a non-porous gas permeable polymer, making each tube gas permeable, but not dielectric fluid permeable. Diffusion of the fault gases occur through the fiber tubes until equilibrium exists on both sides of the phase barrier. The time required to reach equilibrium or near equilibrium conditions depends upon factors such as pressure and temperature, the size of the diffusing molecules and the permeation properties of the media, as well as the flow rate of the oil carrying the gases for equilibrium.
U.S. Pat. No. 8,347,687 to Cunningham describes an apparatus for performing dissolved gas analysis on electrical insulating oil which makes use of photo-acoustic spectroscopy (PAS) to analyze the fault gases. The apparatus includes a gas extraction module in which the fault gases are released from the oil by means of an agitator into a head space of the module. After a period of agitation, head space equilibrium is achieved, and the gases are pumped into an analysis cell where measurements of the head space gases are performed with a PAS module. The apparatus conveniently includes a fluid conduit configuration which enables the measure of oil samples from different sources relatively easily while minimizing or avoiding cross contamination.
A deficiency associated with many commonly used apparatuses used for performing dissolved gas analysis on electrical insulating liquid (such as for example electrical insulating oil) is that they frequently use infra-red absorption methods that require relatively large sample gas volumes to be able to detect the minimal concentrations of fault gases that are relevant for detecting emerging faults in liquid-insulated electrical equipment. For example, such minimal concentrations may represent gas levels as low as 1 ppm in the case of acetylene. The requirement for relatively large sample gas volumes, however, increases manufacturing costs of other systems in the apparatus, including those required to maintain the liquid/gas samples within a specific operational temperature range to ensure measurement accuracy and reproducibility. In addition, the relatively large sample gas volumes required often lead to increases in the period of time required to extract the fault gases from each sample (i.e., the time required to reach equilibrium), which negatively impacts the time-resolution and accuracy of dissolved-gas concentration measurements of many conventional DGA apparatuses.
Against the background described above, it is clear that there remains a need in the industry to provide improved dissolved gas analysis apparatuses and methods that alleviate at least in part the deficiencies of the existing apparatuses and methods.